The present invention relates to a laminated glass and a window, and more particularly to a vehicle window in which the escape through the window in case of emergency is considered.
Recently, public attention has been paid to the fact that not a few people are killed in automobile accidents in which automobiles fall into the sea, rivers, reservoirs, lakes and the like. For example, in Japan, 200 to 250 people lose their lives every year in automobiles sunk in water as reported in an article of the morning edition of the Osaka Yomiuri of Jul. 5, 1997.
As described in this article, an automobile can usually float on water for several minutes when falling into the sea or the like. The driver and passengers in the automobile have to escape while the automobile is still on the surface of the water. However, the doors of the automobile partially subjected to the external water pressure (the water pressure reaches as high as about 100 kgf) cannot be easily pushed open. The occupants trying to escape by opening a window often find an electrically powered window inoperative due to the entrance of water. Furthermore, for an automobile glass, the use of a tempered glass sheet or a laminated glass sheet which are not easily broken by hand alone is mandatory to ensure the safety of the people in the automobile in case of an automobile crash or the like.
Thus, in order to obtain an escape route by cracking a window glass in case of emergency, it is recommended to keep a hammer for breaking glass in an automobile. In Japan, sales of such hammers at automobile equipment stores have increased, partially because the Ministry of Transport announced their necessity.
A hammer for breaking glass comprises a special pointed steel part at its tip and is used to provide an escape route for the occupants in an automobile by utilizing the properties of a tempered glass sheet. A tempered glass sheet produced by heat-treatment of a glass sheet is different from the normal glass sheet in breaking. When a blunt object such as a human head hits a tempered glass sheet, it is broken less easily than a normal glass sheet in an untreated state due to a compressive stress layer in the surface of the tempered glass sheet. The compressive stress layer inhibits small cracks in the surface from growing. However, once cracks in the surface extend to the inside by using a keen member such as the tip of the hammer for breaking glass, the cracks propagate spontaneously over the tempered glass due to an internal tensile stress, so that the glass can be easily broken. The heat-treatment for tempering causes not only the compressive stress in the surface but also the tensile stress under the surface.
On the other hand, like tempered glass, a laminated glass also is widely used as an automobile window glass. Generally, the laminated glass comprises two non-tempered glass sheets bonded with a plastic intermediate film such as PVB (polyvinyl butyral resin). The laminated glass provides excellent safety in that when a human body hits the glass, the glass itself cracks and is deformed while preventing the human body from being thrown out, thus averting injuries to the human body with the broken pieces of the glass and an excessive impact on the human head. The safety is caused by the flexible intermediate film holding the glass sheets or the broken pieces of the glass sheets.
However, the excellent property of the laminated glass provided by the combination of the intermediate film and the glass sheets makes the demolition of the window glass in a short time difficult. Even if the hammer for breaking glass is used, it is not easy to escape through a window in which a conventional laminated glass is fitted. In commercially available automobiles, a laminated glass is used for a windshield, while for other windows such as side windows tempered glass sheets are generally used. However, the use of a laminated glass for the other windows is expected to increase because of its excellent function in safety.
Therefore, it is an object of the present invention to provide a laminated glass that can reduce difficulties in escaping from the interior of an automobile or the other vehicles and an automobile window that reduces the difficulty of the escape.
In order to achieve the above object, an embodiment of the laminated glass of the present invention comprises a first glass sheet, a second glass sheet and an intermediate film for bonding the glass sheets. The first glass sheet is a tempered glass in which, by breaking the first glass sheet at one point, cracks spread spontaneously from the point so that a crack-network is formed in the first glass sheet. On the other hand, the second glass sheet has a lower strength than the first glass sheet.
According to the laminated glass, the difficulty in escaping from the interior of a vehicle such as an automobile can be reduced. The first glass sheet is a tempered glass sheet in which by breaking the glass sheet at one point with a hammer for breaking glass or the like, cracks can run spontaneously while breaking up into some branches, so that the cracks form a mesh-like pattern and the glass sheet is easy to be broken into many pieces. The second glass sheet has a relatively low strength, so that the difficulty of breaking through the intermediate film is reduced. After dividing the first glass sheet into many small pieces, the difficulty in breaking the second glass sheet through the intermediate film can be reduced further.
In such a laminated glass, it is preferred that the second glass sheet is not subjected to heat-treatment for tempering to such an extent that cracks run spontaneously when breaking the glass sheet at one point. More preferably, the second glass sheet is a non-tempered glass sheet. When the second glass sheet has a thickness of 1.5 to 3.2 mm, the difficulty of the demolition through the intermediate film can be further reduced. Herein, the non-tempered glass sheet includes all glass sheets except for tempered glass sheets wherein a compressive stress layer is formed on the surface by heating the glass sheet to around its softening point and quenching it. A tempered glass sheet usually has a strength three to five times that of the glass sheet before tempering.
Another embodiment of the laminated glass of the present invention comprises a first glass sheet, a second glass sheet and an intermediate film for bonding the glass sheets, and the laminated glass satisfies the following equations:
F1xe2x89xa7xe2x88x928.5(t1xe2x88x922.0)+55,
2.0xe2x89xa6t1xe2x89xa64.0,
F2xe2x89xa6xe2x88x929.41(t2xe2x88x921.5)+44,
and
1.5xe2x89xa6t2xe2x89xa63.2,
wherein t1 [mm] is the thickness of the first glass sheet, F1 [MPa] is the residual tensile stress in a cross-sectional center of the first glass sheet, t2 [mm] is the thickness of the second glass sheet, and F2 [MPa] is the residual tensile stress in a cross-sectional center of the second glass sheet.
According to such a laminated glass, the difficulty in escaping from the interior of a vehicle such as an automobile can be reduced. The above formulae were found as a result of various experiments based on a novel viewpoint that the thickness of the glass sheets and the relationship between the thickness and the internal stress are the primary factors to be considered for reducing difficulties in escaping from the interior of a vehicles.
Still another embodiment of the laminated glass of the present invention comprises a first glass sheet, a second glass sheet and an intermediate film for bonding the glass sheets. The first glass sheet is a tempered glass in which, by breaking the first glass sheet at one point, cracks spread spontaneously from the point so that a crack-network is formed in the first glass sheet. In the laminate glass, an edge of the first glass sheet protrudes over an edge of the second glass sheet.
According to the laminated glass, the difficulty in escaping from the interior of a vehicle such as an automobile or the like can be reduced. The first glass sheet is a tempered glass sheet in which by breaking the glass sheet at one point with a hammer for breaking glass or the like, cracks can run spontaneously while breaking up into some branches, so that the cracks form a mesh-like pattern and the glass sheet is easily to be broken into many pieces. Furthermore, due to the protrusion of an edge of the first tempered glass sheet from the edge of the laminated glass, window frame members can be supported mainly with the tempered first glass sheet that can be easily broken by the hammer or the like.
In the specification, a crack-network means a pattern of cracks in which there are cracks (secondary cracks) extending between and connecting other cracks such as primary crack extending from the breakage point. The crack-network preferably divides the glass sheet into many pieces.
An embodiment of the window of the present invention comprises one of the laminated glasses as described above. In such a window, the first glass sheet preferably faces the interior side, while the second glass sheet faces the exterior side.
It is preferred that the laminated glass is supported substantially only with the first glass sheet at least in a part of a peripheral portion of the laminated glass.
According to such a window, the laminated glass is easily dropped out of the window frame members by breaking only the tempered glass sheet facing the interior side, so that the difficulty of the escape from the window of a vehicle such as an automobile can be further reduced.